Generally speaking, the backlight modules can be divided into an edge lighting type and a bottom lighting type based on the screen sizes. These two types are introduced as follows.
The light source of the edge lighting type is located on a single edge or dual edges for emitting light laterally from the side edge(s) as shown in FIG. 1. The light guiding board 1 is manufactured by cutting or by molding without printing. Usually, the edge lighting type is adopted for the design of the backlight module with the screen size smaller than 20 inch with the characteristics of light weight, slim shape and narrow frame. The edge lighting type is adopted as the main stream design for the backlight modules for cellular phones, personal digital assistants, lap top computers and monitors of desk top computers.
For backlight modules with ultra large screens, the edge lighting type cannot provide any advantage on the aspects of weight, power and brightness. Therefore, the backlight module of the bottom lighting type is developed with the light source disposed right below the screen without the light guiding board. For the bottom lighting type, the light from the self-emitting source, e.g. fluorescent lamp, light emitting diode (LED), etc., passes through the diffusion plate upwards, is evenly distributed and is emitted from the front surface of the screen. Since the room to accommodate the light sources becomes larger for the bottom lighting type, more lamps can be used depending on the screen size of the LCD panel. However, by using such configurations for the bottom lighting type, the thickness, weight and consumed power of the backlight module are increased.
The light guiding board is an important component to affect the is illuminating efficiency in view of the illuminating structure of the backlight module of the edge lighting type. Currently, there are two processes for manufacturing the light guiding board in the industry. One manufacturing process adopts the injection molding technique for molding the poly(methyl methacrylate) (PMMA) grains after being melted under high temperature. The other manufacturing process is done by cutting the large flat PMMA plate and by printing the material, e.g. SiO2 and TiO2, with high reflection and low absorption onto the bottom surface of the PMMA plate to form dots by using silk screening printing method. The Table 1 for comparing these two processes is listed as follows.
TABLE 1Printed lightguiding plateNon-printed light guiding plateProcessing for dotsIntegralCutting a rawforming ofCutting the raw plate forplate for post silkshape &post-processingscreening printingdotsContactUVSolventInjectionNon-contact(ThermalDot typebasebasemolding(Laser)forming)OpticalX◯◯Δ◯efficiencyOptical◯◯ΔXΔmodification& elasticityProductionΔX◯ΔΔopticalstabilityProduction◯◯ΔΔXdimensionalstabilityProduction◯◯XXΔcapacity perunit timeFacility cost◯ΔXΔXDeveloping◯◯XΔΔcapabilityfor large sizeDevelopingΔX◯XXcapabilityfor wedgeboardwhere the symbol “◯” denotes “excellent”, the symbol “Δ” denotes “fair”, and the symbol “X” denotes “poor”.
Unfortunately, when the edge lighting type is adopted for the backlight module based on the screen size and when the LEDs are used as the light sources, the issue of non-uniform illumination often occurs no matter a printed light guiding board or a non-printed light guiding board is used, due to the diffusion angle of the illumination for the LED. The positions located within the diffusion angle of the LED and close to the LED are brighter; while the positions located at a middle point between two LEDs and at the edge are darker.
Currently, there are two technical strategies to solve the issue. For the first strategy, the light sources are treated by using the optical cup or lens to enlarge the diffusion angle of the illumination for the LED, or by aligning several LEDs in a row to allow the overlaps of the diffusion angles among the several LEDs so as to look like a linear light source, e.g. cold cathode fluorescent lamp, or by disposing several LEDs at the corner with multiple illumination angles, so as to increase the uniformity of the illumination of LEDs and to diminish the dark band in the edge. However, all these methods will raise the cost. For the second strategy, the surface of the light guiding board is treated to break the total internal reflection and to allow the light to pass through the surface. The bottom of the light guiding board is introduced with the diffusion dots distributed at various densities over the bottom. These diffusion dots can be manufactured by ink painting, chemical etching or other methods. Since the light intensity is higher at the positions close to the light sources, the diffusion dots at these positions are designed to have smaller sizes and lower densities, and vice versa. In addition, the alignments of the diffusion dots are designed by disposing the diffusion dots in the concentric distribution or in sectional distribution to adjust the longitudinal and transverse densities, so as to adjust the brightness of the place close to the light source and to compromise the brightness insufficiency in the edge by setting the different density of dots according to the light energy distributions of the LEDs.
However, as the panel size is increased, e.g. larger than 37 inch, the size of the light guiding board is increased. For the light guiding board with such a large size, the technical strategy of forming the diffusion dots at the bottom of the light guiding board may fail.
Therefore, the present invention provides a customizable laser processing apparatus able to be used for large size panels for forming dots on the surface of the light guiding board with excellent uniformity on the appearances, radii and depths of the dots.
For overcoming the mentioned drawbacks existing in the conventional techniques, a customer-adjustable laser processing apparatus is provided based on the inventive concept of the present invention regarding the large dimensional panel and the forming of dots on the surface of the light guiding board by controlling the shapes, radii and depths of the dots for reflection.